1. Field of the Invention:
This invention relates to a drive apparatus for a hybrid vehicle having an engine and a driving motor, and more particularly to the treatment of exhaust gas produced when the engine is activated.
2. Description of the Related Art:
In recent years, for the purposes of air environment protection and noise reduction, a so-called electric vehicle equipped with an electric motor as a drive source has commanded a lot of attention. However, a battery to activate the electric motor has only a limited capacity so that the electric vehicle can travel only a limited distance on one battery charging, compared to gasoline vehicles. Further, unlike filling up with gasoline, it takes a long time to charge up the battery of the electric vehicle so that it is impossible to increase uninterrupted mileage to a considerable extent.
To this end, a hybrid vehicle has been proposed which suppresses the exhaust gas and noise problems of the conventional gasoline vehicles and complements the disadvantage of the electric vehicles. In this hybrid vehicle, a generator is activated by the engine to supply electricity to a motor for driving the vehicle and also to accumulate electricity in a battery. In the hybrid vehicle, like the conventional electric vehicle, the battery can supply electricity to the motor for driving the vehicle. Further, since variance in output torque can be damped by the battery, it is possible to operate the engine in a constant condition, irrespective of the travelling conditions of the vehicle. It is therefore possible to operate the engine so as to cause less noise and less noxious substances to be contained in the exhaust gas.
FIG. 5 of the accompanying drawings shows, of the prior hybrid vehicles, a so-called series hybrid vehicle. The series hybrid vehicle comprises an engine 1 to be driven by fuel such as gasoline, a generator 2 to be activated by the engine 1 to generate d.c. electricity, a battery 3 for accumulating the electricity generated by the generator 2, an inverter 4 for converting the d.c. electricity from the generator 2 and the battery 3 into a needed value of a.c. electricity, an induction motor 6 to be activated by the a.c. electricity from the inverter 4, and a transmission or gearbox 7 for transmitting the driving force of the motor 6 to tires 8.
During power running, fuel such as gasoline is supplied to the engine 1 for rotation at a predetermined r.p.m. The torque of the engine 1 is transmitted to the generator 2 for conversion into d.c. electricity. Of the thus obtained electricity, an amount sufficient to drive the motor 6 is sent to the motor 6 via the inverter 4 and the surplus electricity is accumulated in the battery 3. On the other hand, the torque of the motor 6 is transmitted to the tires 8 via the transmission 7 to cause the hybrid vehicle to travel. When the electricity sent to the motor 6 from the generator 2 is short, the battery 3 supplies the shortage. The supply of electricity to the motor 6 is varied by controlling a built-in switching device of the inverter 4 to react accordingly to the extent of stepping on the accelerator or gas pedal.
On the other hand, to lower the speed of the hybrid vehicle, regenerative braking is used as a counterpart to engine braking. Regenerative braking is performed as the switching device built into the inverter 4 is controlled. During this regeneration, rotational energy is given to the motor 6 from the tires 8 via the transmission 7. Regenerated electricity is produced from the motor 6. This regenerated electricity is converted into d.c. electricity by the inverter 4, and is then accumulated in the battery 3.
As mentioned above, the hybrid vehicle carries the engine 1. Whenever the engine 1 is operated, it produces exhaust gas; consequently the most important subject currently is to realize low environmental pollution by minimizing air polluting substances in the exhaust gas.
The emission of air polluting substances in the exhaust varies sharply as the operating condition of the engine 1 is changed. For example, if the engine 1 is started at the beginning of operation when it is low in temperature (cold starting), the emission of air polluting substances is increased very much. Usually the vehicle is equipped with an exhaust gas cleaner called a catalytic converter; if this catalytic converter works adequately, the exhaust gas contains only a very small amount of air polluting substances. If it is low in temperature, however, the catalytic converter works inadequately so that the emission of air polluting substances such as hydrocarbon (HC) is increased. Thus if an engine-related part or element, such as the engine body or the catalytic converter, is low in temperature, air polluting substances in the exhaust gas are increased.
Japanese Utility Model Publication No. SHO 56-17724 discloses a concept of warming up the engine using the electricity from the battery. In this prior art, since a heater dedicated for warming-up is used, it is impossible to use regenerated electricity efficiently.